The invention relates to a safety device for stopping the operation of a kneading machine which is used for kneading a seal rubber material, when a hand of the worker or the like enters a hazardous region between two rolls.
When materials of two or more kinds are to be kneaded, a method is usually employed in which the materials are supplied into a gap between two rolls laterally juxtaposed. For a rubber material, particularly, a method in which various materials such as base rubber, a reinforcing material, and a vulcanizing agent are kneaded by rolls is widely employed. As shown in FIG. 12, in a kneading machine 11, two rolls 12 which are laterally juxtaposed are disposed so that their peripheral side faces are close to each other, and the rolls 12 are rotated in such a manner that movements of both of their opposing peripheral side faces are downward directed. The rolls 12 are disposed above a catch pan 24 on a pedestal 13, and their rotary shafts are rotatably supported at the end portions by side plates 15 which are upward projected from edge portions of the pedestal 13. As shown in FIG. 13, the shafts of the rolls 12 are coupled to a motor 17 through a transmission device 16, so as to be rotated. In this configuration, the one of the rolls 12 which is closer to the worker A in FIG. 12 is rotated faster than the other roll. An electric heater which is not shown is incorporated for heating in each of the rolls 12. A partition moving bar 18 elongates above the rolls 12 so as to pass through two partition plates 19 in such a manner that the plates can be slidably moved along the axial direction of the rolls 12. The positions of the partition plates 19 can be fixed by means of screws of grips 20, respectively.
The worker A who conducts the kneading work charges a rubber material B into which raw materials are mixed, into the space between the partition plates 19 from the top of the kneading machine 11. With the rotation of the rolls 12, thereafter, the rubber material B is downward transported through the gap between the rolls and then discharged toward the worker A along the peripheral face of the roll 12 which is closer to the worker and rotated faster. The worker A catches the discharged rubber material B by hands and again charges the material into the space between the partition plates 19 from the top of the machine. The rubber material B is kneaded by repeating the above-mentioned works. In order to knead the material uniformly and sufficiently, the worker A conducts the recharging work in the following manner. The discharged rubber material B is wound into a cylindrical shape and the cylindrical rubber material B is laterally recharged. Alternatively, the discharged rubber material B is severed with a knife and then the severed material is recharged. During the kneading work, the screws of the grips 20 are loosened and the distance between the partition plates 19 is adjusted as required.
Even in the case where the rubber material B is kneaded, the gap between the rolls 12 of the kneading machine 11 is as small as about several millimeters. When the rubber material is to be finally shaped into a thin sheet, the gap is set to be very small or about 1 mm. When a hand of the worker A excessively reaches the gap between the rolls 12 during the work of charging the rubber material B into the space between the partition plates 19 while carrying the rubber material by hands, therefore, there arises a danger that the hand is caught in the rotation and squeezed into the narrow gap.
To comply with this, as shown in FIG. 12, the conventional kneading machine 11 is configured so that a touch bar 31 is disposed above the rolls 12 or a microphone 32 is disposed. The touch bar 31 is connected to a safety device which detects an operation of the touch bar by means of a limit switch placed in the base and then interrupts the power supply of the motor 17. When a hand of the worker A is caught between the rolls 12, therefore, the worker can push or pull the touch bar 31 by the other hand, so that the rotation of the rolls 12 is immediately stopped. The microphone 32 is connected to a safety device which detects an input caused by a loud sound and then interrupts the power supply of the motor 17. When a hand of the worker A is caught between the rolls 12 and the worker screams, therefore, the rotation of the rolls 12 is immediately stopped in response to this.
In some cases, an emergency rope is stretched in place of the touch bar 31 and the rope is connected to a safety device which detects an operation of pulling the emergency rope and then interrupts the power supply of the motor 17.
The prior art safety devices are configured so as to immediately stop the rolls 12 in the case where the touch bar 31 or the like is operated when a hand of the worker A is caught and the worker fears danger or the hand is actually squeezed, or the case where the worker A screams when a hand is caught. The safety devices operate only to enable a countermeasure to be taken immediately before a serious accident happens or after such an accident occurs, and have a problem in that such devices cannot prevent an accident from occurring.